1. Field of Invention
This invention relates to writing instruments which contain an eraser dispenser mechanism.
2. Description of Prior Art
There exist writing instruments, such as conventional mechanical pencils where the lead can be protracted or retracted with a hocking action, which also contain an eraser dispenser.
There are three general versions of such writing instruments. Two of these versions merely involve attaching an eraser dispenser to the back end of a shortened writing instrument of the conventional design, with some means provided to convey a knocking action to the front of the instrument. In the third version, the lead advancement mechanism and the eraser extension mechanism are part of a refill which is held within the shell of the writing instrument.
U.S. Pat. No. 5,022,774 to Kageyama et al. (1991) shows an example of the first of these versions, in which an outercasing of a mechanical pencil is made up of two sections. A rear outercasing section is rotatably and axially slidably connected to a front outercasing section. Within the rear outercasing is a spiral groove. An eraser holder has an outward diametric projection which engages the eraser holder with the spiral groove. The eraser holder is nonrotatably connected to, but is axially slidable with, the front outercasing. The extension or retraction of the eraser is accomplished by rotating the rear outercasing relatively with the front outercasing. There is a lead pipe axially slidably inserted within the front outercasing. The lead pipe serves as a conveyance of the knocking motion and stores any extra leads, in the conventional manner. A forward knocking motion of the rear outercasing knocks the lead pipe, which in turn, in the conventional manner, advances the lead. The lead pipe is returned to the non-knocking position by an elastic member in the front of the pencil, in the usual manner.
This first version has the disadvantage that the outercasing must be made up of two sections. The rear outercasing must be at least as long as the eraser, and as the purpose of the device is to provide a long eraser, the rear outercasing is relatively long. During knocking, this long rear outercasing forces the operator to grip the pencil towards the front, and it is difficult to knock the distant tail with a finger from the same hand that grips the front outercasing; frequently the hand interferes with the knocking motion. Thus, knocking is most easily accomplished by a two handed operation, in which each section must be gripped. This is difficult in comparison to the easy, single-handed, knocking process of conventional mechanical pencils where the pencil can be gripped as far back, with one hand, as is convenient.
Another disadvantage of this version is that replacing the leads is complicated. The rear outercasing must be separated from the front outercasing. This process exemplifies the failure to achieve a comprehensive unification of the eraser dispenser and writing instrument.
Another disadvantage of the first version is that the eraser holder takes up some space between the front end of the eraser and the rear end of the lead pipe, thus reducing the length of eraser that can be used in the pencil.
Yet another disadvantage of this first version is that the increased wall thickness of the rear outercasing needed for the spiral groove either restricts the diameter of the eraser or forces the rear outercasing to be large and unsightly.
Yet another disadvantage of the first version is that there are many parts which must be manufactured and assembled.
Yet another disadvantage of this version is that the outercasing section is comprised of two complicated elements and thus restyling the writing instrument by interchanging outercasings is costly and difficult.
U.S. Pat. No. 5,018,891 to Kageyama et al. (1991) shows an example of the second version of writing instruments with an attached eraser dispenser. This version solves the problem of a hand, which is gripping the pencil, interfering with the knocking motion. In this mechanical pencil, a tubular eraser holder has an inward aliametric projection which engages a spirally grooved shaft running axially within the eraser holder. The spirally grooved shaft is relatively nonrotatable with the outercasing. The eraser holder has an outward aliametric projection which engages a longitudinal groove within the inside of a tubular eraser guide. The eraser guide is axially slidable and rotatable within the rear end of the outercasing of the pencil, and extends beyond the end of the pencil enough to be gripped by fingers. The extension or retraction of the eraser is accomplished by rotating the eraser guide relatively with the outercasing of the pencil. The outercasing is comprised of two pieces, threadably connected. The spirally grooved shaft has a limited range of axial motion within the outercasing; an elastic member resists the spirally grooved shaft's forward motion and an annular inward projection within the outercasing prevents the spirally grooved shaft's rearward motion beyond a certain point. There is a lead pipe axially slidably inserted within the front outercasing, with a knocking cap on the rear end. The lead pipe serves as a conveyance of the knocking motion and stores any extra leads, in the conventional manner. A forward knocking motion of the eraser guide knocks the spirally grooved shaft, which in turn knocks the lead pipe, which in turn, in the conventional manner, advances the lead. The spirally grooved shaft is pushed rearward, allowing the lead pipe to return to the non-knocking position, by the aforementioned elastic member pushing rearwardly against the spirally grooved shaft.
A significant disadvantage of this second version is that the spirally grooved shaft, being at least as long as the desired axial motion of the eraser holder, is incorporated between the end of the lead pipe and the eraser. Thus the length of eraser that can be used in this pencil, for a given pencil length, is shorter than if the spirally grooved shaft could be removed without loss of capability. Since the desired axial motion is as long as the eraser, removal of the spirally grooved shaft without loss of other capability would double the amount of usable eraser in the device.
Another disadvantage of this version is that replacing the leads is complicated. The rear outercasing must be unscrewed from the front outercasing and then a knocking cap must be removed. This process exemplifies the failure to achieve a comprehensive unification of the eraser dispenser and writing instrument.
Another disadvantage of this version is that there are many parts which must be manufactured and assembled.
Yet another disadvantage of this version is that the outercasing section is comprised of two complicated sections and thus restyling the writing instrument by interchanging outercasings is costly and difficult.
Japanese patent 82600 to Koji Sakaoka (1991) is an example of the third version of writing instruments with an eraser dispenser. In this version, the lead advancement mechanism and the eraser dispenser are part of a refill to be inserted inside the body of a writing instrument. The body of the writing instrument is made up of two sections, or barrels. The front and rear barrels can rotate relatively but are not axially slidable. The refill, contained or inserted within the body of the writing instrument, has a lead pipe on its front, and attached to the front of the lead pipe is a typical lead advancement mechanism. The rear portion of the refill, attached to the rear end of the lead pipe, is a spirally grooved tube, with two diametrically opposed longitudinal slots in it. This spirally grooved tube interfaces with the front portion of the outer barrel of the writing instrument in such a way that they cannot rotate relatively. Inside the spirally grooved tube is an eraser holder, holding an eraser which is also inside the spirally grooved tube. Outside of the spirally grooved tube is a moving ring. The moving ring engages the eraser holder through the longitudinal slots in the spirally grooved tube. Thus, when the moving ring moves along the outside of the spirally grooved tube, the eraser holder and eraser move accordingly within the spirally grooved tube. The moving ring has an inward curved projection which engages the grooves of the spirally grooved tube so that when they are relatively rotated the moving ring moves along the spirally grooved tube. The moving ring also has two outward projections which axially slidably engage two guide grooves within the rear outer barrel of the writing instrument so that the moving ring and the rear outer barrel cannot rotate relatively. Thus, when the rear outer barrel and the front outer barrel are relatively rotated, the moving ring and the spirally grooved tube are also relatively rotated, and the moving ring moves along the outside of the spirally grooved tube, thereby extending or retracting the eraser.
The main goal of this design is that both the lead advancement mechanism and the eraser dispenser mechanism, comprising a refill, can be removed for cleaning, repair, or replacement.
There are, however, disadvantages to the refill version. The most significant of these is that the spirally grooved tube occupies substantially the same region that the eraser is stored in, and thus the diameter of the eraser is severely restricted. Since the volume of the eraser, for a given eraser length, increases as the square of the eraser radius, the amount of eraser this pencil provides is significantly limited. Another way in which this pencil limits the amount of eraser is that the eraser holder occupies some space between the end of the stored leads and the beginning of the eraser, and thus restricts the length of the eraser.
Another disadvantage of this version of mechanical pencil with an eraser dispenser is that there are many complicated interconnecting parts, which greatly increases the cost of manufacture.
In summary, the prior art in the field of adjustable writing instruments with eraser dispensers leaves several disadvantages:
(a) The outercasing of the writing instrument comprises two axially moveable sections in such a manner that the knocking process is complicated by the hand gripping the pencil.
(b) Spiral grooves, or spirally grooved elements, within the rear outercasing either restrict the diameter of the eraser or force the tail of the pencil to be large and unsightly.
(c) The length of erasers that can be used in these writing instruments is restricted by members between the front end of the eraser and the rear end of the lead pipe. The prior art invention which solves disadvantages (a) and (b) has a significant restriction in eraser length.
(d) The lead replacement process is complicated and requires the separation of the outercasing into two sections.
(e) The manufacture and assembly of these writing instruments is expensive and complicated due to the multitude of small interconnecting parts.
(f) The manufacture and assembly and restyling of these writing instruments is costly and complicated due to the plurality of complicated outercasing sections.